Automatic Retarding Control (ARC) System Schematics
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| Illustration 1 | g03657178 |
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Schematic of the retarding system lever and brake oil axle temperature sensors connected to the transmission ECM | |
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| Illustration 2 | g03657250 |
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Schematic of arc solenoids and brake oil tank temperature sensor connected to the chassis ECM | |
Retarding System Lever Function
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| Illustration 3 | g06198778 |
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Retarding system lever on steering column (right side) (1) Column Switch Assembly | |
The Retarding System Lever is located to the right side of the steering column. The control lever switch has four positions:
- OFF (0) position – When the lever is in position (0), the retarding system is disabled.
- MEDIUM (I) position – Move the lever to manual mode position (I) to enable "4-cylinder" engine compression braking.
- HIGH (II) position – Move the lever to manual mode position (II) to enable "6-cylinder" engine compression braking.
- AUTO (III) position – Move the lever to position (AUTO) to enable the Automatic Retarding Control (ARC) system. The Transmission ECM modulates the ARC solenoids to maintain operator set machine speed.
The ARC utilizes the engine compression brake for primary retarding and the electrohydraulic wheel brakes as secondary retarding.
Note: The wheel brakes are only applied when the retarding system is in the Auto mode.
The engine compression brake is applied to the highest level needed or requested. The electrohydraulic wheel brakes are used to:
- Slow the machine to the appropriate retarding gear for the specific grade and payload.
- Supplement power gaps in discrete engine brake levels.
The wheel brakes are commanded through two solenoid valves:
- The Rear valve controls the brakes on the center and rear axles.
- The Front valve controls the brakes on the front axle.
Note: Pressure is applied to all brakes equally.
The retarding system is activated by selecting the desired Retarding System lever position and releasing the throttle pedal. The lockup clutch must be engaged for the retard function to be active, and will be requested if not already engaged.
When using manual mode, the engine compression brake is commanded to the level requested through the Retarding System lever. The Transmission ECM uses datalink signals to determine the appropriate time to engage the retarder. On flat or uphill grades, the retarder will activate only in gears equal to or greater than fifth gear. On downhill grades, the retarder will engage in any gear.
When using Auto mode during flat ground operation, the engine compression brake is commanded to discrete levels based on payload and transmission gear. With machine loaded, at higher speeds, the engine brake is commanded too High. As the machine slows down, the engine brake lowers to Medium at lower gears. When the machine reaches fourth gear, the retarding system is deactivated. With the machine empty, the engine brake is commanded to Medium throughout speed range until forth gear is reached. When the machine reaches fourth gear, the retarding system is deactivated. If excessive deceleration is determined by the transmission ECM controls, the engine brake level is lowered by one increment.
When using the Auto mode during downhill operation, a hold speed is set to the current machine speed at which the operator releases the throttle. This speed is maintained automatically by modulating the available retarder(s). A minimum and maximum allowable speed is applied to each transmission gear.
Applying part throttle increases the hold speed, and a higher speed is set when the throttle pedal is released. If the throttle pedal is pressed beyond the throttle pedal position threshold, the retarding system is deactivated. The throttle pedal position threshold is determined based on grade force. A higher threshold is used when operating on steeper grades with a loaded machine, requiring a heavier throttle application. Only light pedal application is needed on shallow grades to deactivate ARC. Applying the brake pedal to decelerate the machine will decrease the hold speed, and a lower speed is set when the brake pedal is released.
After activating Auto mode during downhill grade operation, the Transmission ECM determines the optimum retarding gear for the grade and payload. If a lower gear is required to meet the retarding performance capability, downshifts are commanded. Hold mode or part throttle may be used to prevent downshifts during ARC operation.
A brake temperature strategy is in place, which includes the following features:
- Monitoring the brake oil temperature of the Brake Cooling Tank.
- Monitoring the brake oil temperature of the Front, Center, and Rear Brakes.
When the temperature of the Brake Oil Cooling Tank is equal to or greater than
When any of the axle brake oil temperatures is equal to or greater than
Also, as ARC is automatically applying the wheel brakes to maintain machine speed, if power absorption is high, a dynamic temperature threshold for the tank and the axle brakes can trigger a downshift of the transmission. This temperature threshold is based on machine speed, grade (slope), and payload. If the machine operation is exceeding the machine retarding performance capability, then the automatic application of the wheel brakes is generating excessive energy, and will need to command a downshift of the transmission.
The machine radiator fan will be commanded to maximum speed to aid in brake oil cooling. When any of the axle brake oil temperatures is greater than
Note: The Transmission ECM only commands a downshift when the retarding system is in Auto mode.
Note: The retarding performance guidelines are on a film inside the cab and in the Operation and Maintenance Manual. This film is for sea level operation only. At moderate to high altitude, a slower speed and lower gear should be used.
Retarding System Display Function
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| Illustration 4 | g06198765 |
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Location of retarding system indicators (2) Retarding System Active Indicator (3) Retarding System Fault Indicator | |
Retarding system active indicator (2) is displayed on the LCD display in the bottom right corner. When ARC is active by using the Auto position, the automatic retarding icon is displayed. When Medium or High retarding level is active by using the lever positions, the manual retarding icon is displayed.
The fault status of the retarding system is displayed in the lower left corner of the gauge cluster display. If the system is faulted due to a loss of signal, the dash lamp illuminates amber. The engine compression brake will default to 6-cylinder braking. Use Cat ET to check for active diagnostic codes when the system is faulted.
If the Retarding System Lever is faulted, the Transmission ECM will assume the AUTO position. The operator will not be able to disable the retarding system. The fault status lamp will not illuminate. Under these circumstances, use Cat ET to check for active diagnostic codes.